In the medical and pharmaceutical fields, there has been a need for portable and wearable injector of mini size capable of injecting a small quantity of an infusion liquid, such as a liquid drug, continuously for a long period of time in order to treat diseases, such as cancers, diabetes, sterility, hormonal insufficiency and others. Conventional injectors have utilized a motor as an injecting power source, which makes miniaturization and use of the injectors difficult and inconvenient. Further, such injectors are inconvenient for portability and wearability and very high in cost. In addition, the motor used in the injector requires a relatively large quantity of electric current for driving, which may be supplied only by a large battery.
As injectors of other types without use of the motor, there have been known an injector utilizing a temperature elevation for volumetric expansion or evaporation of a certain substance in the injector syringe to obtain the increased pressure, and an injector utilizing an osmotic pressure. The former injector has a disadvantage of being limited to usage in a specified temperature atmosphere for keeping an injected amount at a constant level, while the latter injector has a problem of inconvenient handling.
Further, the conventional syringe has a large inner cylinder rod for a piston and a grip occupying a half of the syringe volume, which is not usable for the infusion liquid.
Nevertheless, the injection has been carried out intermittently and frequently by means of the conventional types of syringes with the above problems. The intermittent and frequent injections are, of course, troublesome and undesirable for maintaining the proper level of medicine in the blood.
In order to overcome the disadvantages of the conventional injectors as described hereinabove, the inventor has developed and reported a number of microinjectors for injecting the infusion liquid or for protein-analysis [for example, Yamada, Neuroendocrinology 18:263(1975); Yamada, Brain Res. 142:187(1978); Yamada, Endocrinol. Jap. 25:397(1978); Yamada, Brain Res. 172:165 (1979); Yamada, J. Biochem. Biophys. Methods 7:175(1983); Yamada, J. Biochem. Biophys. Methods (in press); Yamada, Proc. Electrophoresis (in press); Yamada, Anal. Biochem. in reform, and others].
It has now been found out that a gas-generating means in an injector may produce a pressure gas within the injector to urge an infusion liquid through a needle attached to one end of the injector, and that an electric or chemical means may be utilized as the gas-generating means. When using the electric means, a generated gas volume by electrolysis of water is directly proportional to an electric current consumed and is 1868 times of volume of water, so that very small quantity of the electric current and very small size of the electric cell are sufficient for the injection purpose.
Accordingly, an object of the invention is to provide a portable and wearable injector of mini-size, which may eliminate the disadvantages of the conventional injectors, such as inconveniently large size, high cost, complicated mechanism requiring a motor with a power source, outer limiting factors (for example, humidity condition), inconvenient handling and others, and which may inject a small quantity of an infusion liquid, such as liquid drug, continuously for long period of time by use of very simple means.